[1]} counts the number of correctly interpreted pairs of vertices (either two vertices belonging to the same community and connected by an edge, or two vertices belonging to different communities and not connected by an edge). For a given partition \(\mathcal {P}\) , we denote by \(\mathcal {C}(u)\)  the community containing vertex \(u\)  in the following definition:
\(Q^P(\mathcal {P}) = \frac{|\lbrace \lbrace u,v\rbrace  \in E, \mathcal {C}(u) = \mathcal {C}(v)\rbrace | + |\lbrace \lbrace u,v\rbrace  \notin E, \mathcal {C}(u) \ne \mathcal {C}(v)\rbrace |}{\frac{1}{2}n(n-1)}\) 
